This invention relates to a DC (direct current) power circuit having two different output characteristics, and more particularly to a DC power circuit responsive to external control for selectively supplying a load with DC power of different characteristics.
A DC power circuit of this kind is known in the art for use as an adapter of a video tape recorder, for example. Such a DC power circuit is arranged to provide an output voltage of a preset level when used to drive the recorder, and to provide an output voltage higher than the present level when recharging a built-in battery of the recorder.
FIG. 1 is a simplified block diagram of a conventional DC power circuit. The DC power circuit of FIG. 1 generally comprises a DC power source 2, circuits 4 and 6 each including a control circuit (not shown), and a switch S. The switch S serves to selectively connect one of the circuits 4 and 6 to one output terminal 8 to obtain desired output currents as well as desired voltages through output terminals 8 and 9. FIG. 2 includes illustrations of output characteristics of the prior art of FIG. 1. Curve C1 denotes one of the two output characteristics in which the output voltage and current are controlled so as to not exceed preset limits V1 and I1, respectively, and curve C2 denotes the output characteristic in which the output voltage and current are also controlled so as to not exceed preset limits V2 and I2, respectively.
In accordance with the prior art, however, each of the circuits 4 and 6 should have a separate control circuit and hence the entire circuit becomes bulky and complicated in arrangement. Additionally, the switch S should have a high voltage rating in that it makes or breaks electrical connections between the control circuits and the output terminals, resulting in high manufacturing cost.